It sounds like you got it going pretty well now. I'd still like to recommend the software from Genki English. Genki English has some great songs based around simple subjects in English that focus on building simple dialogue.
I'd recommend taking it slow. Look at the students' development in their native language. Sure, they are 3...but how are they progressing there? I wouldn't ask my students to do something they can't do in their own language. An example of this is pronunciation. There have been times when my students are saying words/sounds wrong. The parents get a bit upset and want me to correct it. I usually ask the students to say something in their own language that uses that sound. Sometimes, the pronunciation of that particular sound is wrong even in the native language. The parents then let up a little bit.
That said, just don't try to pressure them and give them fun
Seems like you're doing that pretty well so far!